Internal vibrators are known and used to fluidize and consolidate freshly poured concrete layers by high frequency vibrations generated by the internal vibrator. In conventional internal vibrators, the vibrator drive and the imbalance, driven by the vibrator drive, are disposed in the vibrator pipe, which normally is completely immersed into the still liquid concrete layer. The vibrator drive and all support points of the imbalance are thus cooled by the concrete surrounding the external wall of the vibrator pipe, when the internal vibrator is in operation. Overheating of the vibrator drive and of the support of the imbalance are practically impossible.
A transverse pipe is fastened at the bottom end of the vibrator by welding, for better transmission of the high frequency vibration into the concrete, produced by rotation of the imbalance. This transverse pipe increases the effective vibration surface and thus the efficiency of the vibrator, so that the vibrating period necessary for setting of the concrete is noticeably reduced. If however the concrete layer is built up in the course of a two-layer construction process with a bottom concrete layer and subsequently with a concrete layer, the internal vibrators are permitted to dip only into the concrete layer. If the vibrators are immersed also into the bottom concrete layer, there exists the danger that dowels provided in the bottom concrete layer sink excessively towards the bottom and thus do not strengthen the bottom concrete layer in a suitable manner. Furthermore, the two concrete layers would be intermixed with one another in an undesirable manner.
For this reason, conventional vibrators are immersed only with the tip of their vibrators into the concrete layer in the course of the two-layer construction processes and the region of the vibrator pipe containing the vibrator drive is exposed to the atmosphere. In such procedures, high failure rates of the vibrator motor was experienced. The reasons for this can be overheating of the vibrator drive or increased corrosion of the internal vibrator in operation and during subsequent stoppage because of the high temperature differences occurring in the vibrator.
It is therefore an object of the present invention to provide an internal vibrator, where sufficient cooling of the vibrator drive is assured, even with small immersion depth of the internal vibrator into the concrete.